A reconfigurable filter bank system that has an asymmetrical tree structure with multiple stages to generate multiband outputs. Each stage may include cascaded low-pass filters (LPFs), cascaded high-pass filters (HPFs) and/or all-pass filter(s) (APF(s)) having identical phase responses. As the cascaded LPFs, cascaded HPFs and APF(s) have identical phase responses, each frequency band of the multiband output may have an identical phase shift such that the frequency bands are in-phase and can be added together. The multiband outputs of the reconfigurable filter bank may have near-perfect reconstruction (e.g., small number of cross-band ripples) and therefore only minor distortion. In addition, the number of frequency bands and corresponding non-uniform bandwidths (e.g., frequency ranges) may be user-adjustable and/or reconfigurable during device operation. Further, the reconfigurable filter bank may have reduced computational complexity and/or latency.
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1. A computer-implemented method for separating an audio signal into frequency bands using a reconfigurable filter bank to process the frequency bands separately, the method comprising: receiving input audio data corresponding to multiple frequencies; receiving a first crossover frequency value as first input; determining that the first crossover frequency value corresponds to a transition between a first frequency band and a second frequency band; receiving a second crossover frequency value as second input; determining that the second crossover frequency value corresponds to a transition between the second frequency band and a third frequency band; blocking low frequencies of the input audio data that are associated with midrange and bass using a first high-pass filter and a second high-pass filter in series to generate first primary-stage output data, the first primary-stage output data corresponding to frequencies greater than the first crossover frequency value; blocking high frequencies of the input audio data that are associated with treble using a first low-pass filter and a second low-pass filter in series to generate second primary-stage output data, the second primary-stage output data corresponding to frequencies less than the first crossover frequency value; outputting all frequencies of the first primary-stage output data with equal gain using an all-pass filter to generate treble output data, the treble output data corresponding to the first frequency band, the all-pass filter having a first phase response; blocking low frequencies of the second primary-stage output data that are associated with bass using a third high-pass filter and a fourth high-pass filter in series to generate midrange output data, the midrange output data corresponding to frequencies greater than the second crossover frequency value and corresponding to the second frequency band, the third high-pass filter and the fourth high-pass filter in series having a second phase response equal to the first phase response; blocking high frequencies of the second primary-stage output data that are associated with midrange using a third low-pass filter and a fourth low-pass filter in series to generate bass output data, the bass output data corresponding to frequencies less than the second crossover frequency value and corresponding to the third frequency band, the third low-pass filter and the fourth low-pass filter in series having a third phase response equal to the first phase response; generating treble processed data by performing acoustic echo cancellation on the treble output data; generating midrange processed data by performing acoustic echo cancellation on the midrange output data; generating bass processed data by performing acoustic echo cancellation on the bass output data; and generating output audio data by combining the treble processed data, the midrange processed data and the bass processed data.
A computer-implemented method separates an audio signal into frequency bands for separate processing using a reconfigurable filter bank. The method takes input audio data and two crossover frequency values. It uses two cascaded high-pass filters to block low frequencies, creating output data for frequencies above the first crossover (treble). Two cascaded low-pass filters block high frequencies, creating output data for frequencies below the first crossover. An all-pass filter outputs the treble data with a specific phase response. Two cascaded high-pass filters block low frequencies from the low-pass output (midrange), with a matching phase response. Two cascaded low-pass filters block high frequencies from the low-pass output (bass), also with a matching phase response. Acoustic echo cancellation is performed on each band (treble, midrange, bass). Finally, the processed bands are combined to generate the output audio data.
2. The computer-implemented method of claim 1 , further comprising: receiving, during operation of the reconfigurable filter bank, a third crossover frequency value as third input; determining that the third crossover frequency value corresponds to a transition between the third frequency band and a fourth frequency band; outputting all frequencies of the treble output data with equal gain using a second all-pass filter to generate second treble output data, the second treble output data corresponding to the first frequency band, the second all-pass filter having a fourth phase response; outputting all frequencies of the midrange output data with equal gain using a third all-pass filter to generate second midrange output data, the second midrange output data corresponding to the second frequency band, the third all-pass filter having a fifth phase response equal to the fourth phase response; blocking low frequencies of the bass output data that are associated with deep bass using a fifth high-pass filter and a sixth high-pass filter in series to generate upper bass output data, the upper bass output data corresponding to frequencies greater than the third crossover frequency value and corresponding to the third frequency band, the fifth high-pass filter and the sixth high-pass filter in series having a sixth phase response equal to the fourth phase response; and blocking high frequencies of the bass output data that are associated with upper bass using a fifth low-pass filter and a sixth low-pass filter in series to generate subwoofer output data, the subwoofer output data corresponding to frequencies less than the third crossover frequency value and corresponding to the fourth frequency band, the fifth low-pass filter and the sixth low-pass filter in series having a seventh phase response equal to the fourth phase response.
The audio signal processing method of Claim 1 is extended to dynamically adjust frequency bands during operation. It receives a third crossover frequency value. It passes the treble output (from Claim 1) through another all-pass filter. It passes the midrange output (from Claim 1) through another all-pass filter, ensuring matching phase responses. Two cascaded high-pass filters block low frequencies from the bass output (from Claim 1), creating upper bass output. Two cascaded low-pass filters block high frequencies from the bass output, creating subwoofer output. All new filter stages (upper bass, subwoofer) have matching phase responses. This allows real-time adjustment of the filter bank during device operation.
3. The computer-implemented method of claim 1 , wherein, a first stage is associated with the first crossover frequency value and includes the first high-pass filter, the second high-pass filter, the first low-pass filter and the second low-pass filter, first outputs of the first stage having the first phase response, and a second stage is associated with the second crossover frequency value and includes the all-pass filter, the third high-pass filter, the fourth high-pass filter, the third low-pass filter and the fourth low-pass filter, second outputs of the second stage having the first phase response.
In the audio signal processing method of Claim 1, a first filter stage handles the first crossover frequency. This stage consists of two cascaded high-pass filters and two cascaded low-pass filters, all having identical phase responses. A second filter stage handles the second crossover frequency, consisting of an all-pass filter, two cascaded high-pass filters, and two cascaded low-pass filters, all also having identical phase responses equal to the first stage. This architecture ensures phase consistency across the frequency bands generated in each stage of the filter bank.
4. The computer-implemented method of claim 1 , wherein: the input audio data includes a first channel and a second channel, and the treble output data, the midrange output data and the bass output data correspond to the first channel.
In the audio signal processing method of Claim 1, the input audio data contains at least two channels (left and right). However, only one channel (e.g., the left channel) is processed by the treble, midrange, and bass filter bank, and then processed with Acoustic Echo Cancellation (AEC) before combination to output audio data.
5. A computer-implemented method, comprising: receiving input audio data corresponding to multiple frequencies; receiving a first crossover frequency value; determining that the first crossover frequency value corresponds to a transition between a first frequency band and a second frequency band; receiving a second crossover frequency value; determining that the second crossover frequency value corresponds to a transition between the second frequency band and a third frequency band; blocking low frequencies of the input audio data using a first high-pass filter and a second high-pass filter in series to generate first primary-stage output data, the first primary-stage output data corresponding to frequencies greater than the first crossover frequency value; blocking high frequencies of the input audio data using a first low-pass filter and a second low-pass filter in series to generate second primary-stage output data, the second primary-stage output data corresponding to frequencies less than the first crossover frequency value; passing all frequencies of the first primary-stage output data using an all-pass filter to generate first secondary-stage output data, the first secondary-stage output data corresponding to the first frequency band; blocking low frequencies of the second primary-stage output data using a third high-pass filter and a fourth high-pass filter in series to generate second secondary-stage output data, the second secondary-stage output data corresponding to frequencies greater than the second crossover frequency value and corresponding to the second frequency band; and blocking high frequencies of the second primary-stage output data using a third low-pass filter and a fourth low-pass filter in series to generate third secondary-stage output data, the third secondary-stage output data corresponding to frequencies less than the second crossover frequency value and corresponding to the third frequency band.
A computer-implemented method separates an audio signal into frequency bands. The method takes input audio data and two crossover frequency values. It uses two cascaded high-pass filters to block low frequencies, creating first primary-stage output data for frequencies above the first crossover. Two cascaded low-pass filters block high frequencies, creating second primary-stage output data for frequencies below the first crossover. An all-pass filter passes all frequencies of the first primary-stage output. Two cascaded high-pass filters block low frequencies from the second primary-stage output. Two cascaded low-pass filters block high frequencies from the second primary-stage output. The result is three frequency bands after the second primary stage output data is filtered.
6. The computer-implemented method of claim 5 , further comprising: generating first processed data by performing first acoustic echo cancellation processing on the first secondary-stage output data; generating second processed data by performing second acoustic echo cancellation processing on the second secondary-stage output data; generating third processed data by performing third acoustic echo cancellation processing on the third secondary-stage output data; and generating output audio data by combining the first processed data, the second processed data and the third processed data.
The audio signal processing method of Claim 5 adds acoustic echo cancellation to each band's output: The first secondary-stage output data (corresponding to the first frequency band) is processed using first acoustic echo cancellation, creating first processed data. The second secondary-stage output data is processed using second acoustic echo cancellation, creating second processed data. The third secondary-stage output data is processed using third acoustic echo cancellation, creating third processed data. Finally, all three processed signals are combined to generate the output audio data.
7. The computer-implemented method of claim 5 , wherein: the input audio data includes a first channel and a second channel, and the first secondary-stage output data, the second secondary-stage output data and the third secondary-stage output data correspond to the first channel.
In the audio signal processing method of Claim 5, the input audio data contains at least two channels (left and right). However, only one channel (e.g., the left channel) is processed by the filter bank: The first secondary-stage, the second secondary-stage, and the third secondary-stage output data correspond only to the first channel of the input data.
8. The computer-implemented method of claim 5 , wherein a first phase response associated with the third high-pass filter and the fourth high-pass filter is equal to a second phase response associated with the third low-pass filter and the fourth low-pass filter and a third phase response associated with the all-pass filter.
In the audio signal processing method of Claim 5, the cascaded high-pass filters applied to the second primary-stage output data, the cascaded low-pass filters applied to the second primary-stage output data, and the all-pass filter applied to the first primary-stage output data have identical phase responses.
9. The computer-implemented method of claim 5 , further comprising: receiving, during operation, a third crossover frequency value; determining that the third crossover frequency value corresponds to a transition between the third frequency band and a fourth frequency band; passing all frequencies of the first secondary-stage output data using a second all-pass filter to generate first tertiary-stage output data, the first tertiary-stage output data corresponding to the first frequency band; passing all frequencies of the second secondary-stage output data using a third all-pass filter to generate second tertiary-stage output data, the second tertiary-stage output data corresponding to the second frequency band; blocking low frequencies of the third secondary-stage output data using a fifth high-pass filter and a sixth high-pass filter in series to generate third tertiary-stage output data, the third tertiary-stage output data corresponding to frequencies greater than the third crossover frequency value and corresponding to the third frequency band; and blocking high frequencies of the third secondary-stage output data using a fifth low-pass filter and a sixth low-pass filter in series to generate fourth tertiary-stage output data, the fourth tertiary-stage output data corresponding to frequencies less than the third crossover frequency value and corresponding to the fourth frequency band.
The audio signal processing method of Claim 5 is extended to dynamically adjust frequency bands during operation. It receives a third crossover frequency value. It passes the first secondary-stage output data (from Claim 5) through another all-pass filter. It passes the second secondary-stage output data (from Claim 5) through another all-pass filter. Two cascaded high-pass filters block low frequencies from the third secondary-stage output (from Claim 5). Two cascaded low-pass filters block high frequencies from the third secondary-stage output.
10. The computer-implemented method of claim 5 , further comprising: determining, at a first time, a first number of output frequency bands; determining, during operation at a second time after the first time, a second number of output frequency bands; and generating fourth tertiary-stage output data corresponding to a fourth frequency band.
The audio signal processing method of Claim 5 can dynamically change the number of frequency bands during operation. At a first time, the system determines a first number of output frequency bands. At a later time during operation, the system determines a second, different number of output frequency bands. The system generates fourth tertiary-stage output data corresponding to a fourth frequency band.
11. The computer-implemented method of claim 5 , wherein, a first stage is associated with the first crossover frequency value and includes the first high-pass filter, the second high-pass filter, the first low-pass filter and the second low-pass filter, first outputs of the first stage having a first phase response, and a second stage is associated with the second crossover frequency value and includes the all-pass filter, the third high-pass filter, the fourth high-pass filter, the third low-pass filter and the fourth low-pass filter, second outputs of the second stage having the first phase response.
In the audio signal processing method of Claim 5, a first filter stage handles the first crossover frequency. This stage consists of two cascaded high-pass filters and two cascaded low-pass filters, all having a first phase response. A second filter stage handles the second crossover frequency, consisting of an all-pass filter, two cascaded high-pass filters, and two cascaded low-pass filters, all also having the same first phase response.
12. The computer-implemented method of claim 5 , wherein: the all-pass filter is a Butterworth second-order infinite impulse response (IIR) filter; the third high-pass filter and the fourth high-pass filter are Butterworth second-order IIR filters; and the third low-pass filter and the fourth low-pass filter are Butterworth second-order IIR filters.
In the audio signal processing method of Claim 5, specific filter types are used. The all-pass filter is a Butterworth second-order IIR (Infinite Impulse Response) filter. The two cascaded high-pass filters applied to the second primary-stage output data are Butterworth second-order IIR filters. The two cascaded low-pass filters applied to the second primary-stage output data are Butterworth second-order IIR filters.
13. A device, comprising: at least one processor; a memory device including instructions operable to be executed by the at least one processor to configure the device to: receive input audio data corresponding to multiple frequencies; receive a first crossover frequency value; determine that the first crossover frequency value corresponds to a transition between a first frequency band and a second frequency band; receive a second crossover frequency value; determine that the second crossover frequency value corresponds to a transition between the second frequency band and a third frequency band; block low frequencies of the input audio data using a first high-pass filter and a second high-pass filter in series to generate first primary-stage output data, the first primary-stage output data corresponding to frequencies greater than the first crossover frequency value; block high frequencies of the input audio data using a first low-pass filter and a second low-pass filter in series to generate second primary-stage output data, the second primary-stage output data corresponding to frequencies less than the first crossover frequency value; pass all frequencies of the first primary-stage output data using an all-pass filter to generate first secondary-stage output data, the first secondary-stage output data corresponding to the first frequency band; block low frequencies of the second primary-stage output data using a third high-pass filter and a fourth high-pass filter in series to generate second secondary-stage output data, the second secondary-stage output data corresponding to frequencies greater than the second crossover frequency value and corresponding to the second frequency band; and block high frequencies of the second primary-stage output data using a third low-pass filter and a fourth low-pass filter in series to generate third secondary-stage output data, the third secondary-stage output data corresponding to frequencies less than the second crossover frequency value and corresponding to the third frequency band.
A device separates an audio signal into frequency bands. It includes a processor and memory with instructions to: receive input audio data and two crossover frequency values; use two cascaded high-pass filters to block low frequencies, creating first primary-stage output data for frequencies above the first crossover; use two cascaded low-pass filters to block high frequencies, creating second primary-stage output data for frequencies below the first crossover; pass all frequencies of the first primary-stage output data using an all-pass filter; block low frequencies from the second primary-stage output data using two cascaded high-pass filters; and block high frequencies from the second primary-stage output data using two cascaded low-pass filters.
14. The device of claim 13 , wherein the instructions further configure the device to: generate first processed data by performing first acoustic echo cancellation processing on the first secondary-stage output data; generate second processed data by performing second acoustic echo cancellation processing on the second secondary-stage output data; generate third processed data by performing third acoustic echo cancellation processing on the third secondary-stage output data; and generate output audio data by combining the first processed data, the second processed data and the third processed data.
The device of Claim 13 further includes instructions to perform acoustic echo cancellation on each band's output. The first secondary-stage output data is processed using first acoustic echo cancellation. The second secondary-stage output data is processed using second acoustic echo cancellation. The third secondary-stage output data is processed using third acoustic echo cancellation. Finally, all three processed signals are combined to generate the output audio data.
15. The device of claim 14 , wherein: the input audio data includes a first channel and a second channel, and the first secondary-stage output data, the second secondary-stage output data and the third secondary-stage output data correspond to the first channel.
In the device of Claim 14, the input audio data contains at least two channels (left and right). However, only one channel (e.g., the left channel) is processed by the filter bank: The first secondary-stage, the second secondary-stage, and the third secondary-stage output data correspond only to the first channel of the input data.
16. The device of claim 13 , wherein a first phase response associated with the third high-pass filter and the fourth high-pass filter is equal to a second phase response associated with the third low-pass filter and the fourth low-pass filter and a third phase response associated with the all-pass filter.
In the device of Claim 13, the cascaded high-pass filters applied to the second primary-stage output data, the cascaded low-pass filters applied to the second primary-stage output data, and the all-pass filter applied to the first primary-stage output data have identical phase responses.
17. The device of claim 13 , wherein the instructions further configure the device to: receiving, during operation, a third crossover frequency value; determining that the third crossover frequency value corresponds to a transition between the third frequency band and a fourth frequency band; passing all frequencies of the first secondary-stage output data using a second all-pass filter to generate first tertiary-stage output data, the first tertiary-stage output data corresponding to the first frequency band; passing all frequencies of the second secondary-stage output data using a third all-pass filter to generate second tertiary-stage output data, the second tertiary-stage output data corresponding to the second frequency band; block low frequencies of the third secondary-stage output data using a fifth high-pass filter and a sixth high-pass filter in series to generate third tertiary-stage output data, the third tertiary-stage output data corresponding to frequencies greater than the third crossover frequency value and corresponding to a fourth frequency band; and block high frequencies of the third secondary-stage output data using a fifth low-pass filter and a sixth low-pass filter in series to generate fourth tertiary-stage output data, the fourth tertiary-stage output data corresponding to frequencies less than the third crossover frequency value and corresponding to a fifth frequency band.
The device of Claim 13 dynamically adjusts frequency bands during operation. The device receives a third crossover frequency value. The device passes the first secondary-stage output data (from Claim 13) through another all-pass filter. The device passes the second secondary-stage output data (from Claim 13) through another all-pass filter. The device blocks low frequencies from the third secondary-stage output (from Claim 13) using two cascaded high-pass filters. The device blocks high frequencies from the third secondary-stage output using two cascaded low-pass filters.
18. The device of claim 13 , wherein the instructions further configure the device to: determine, at a first time, a first number of output frequency bands; determine, during operation at a second time after the first time, a second number of output frequency bands; and generate fourth first tertiary-stage output data corresponding to a fourth frequency band.
The device of Claim 13 dynamically changes the number of frequency bands during operation. At a first time, the device determines a first number of output frequency bands. At a later time during operation, the device determines a second, different number of output frequency bands. The device generates fourth first tertiary-stage output data corresponding to a fourth frequency band.
19. The device of claim 13 , wherein: a first stage is associated with the first crossover frequency value and includes the first high-pass filter, the second high-pass filter, the first low-pass filter and the second low-pass filter, first outputs of the first stage having a first phase response, and a second stage is associated with the second crossover frequency value and includes the all-pass filter, the third high-pass filter, the fourth high-pass filter, the third low-pass filter and the fourth low-pass filter, second outputs of the second stage having the first phase response.
In the device of Claim 13, a first filter stage handles the first crossover frequency. This stage consists of two cascaded high-pass filters and two cascaded low-pass filters, all having a first phase response. A second filter stage handles the second crossover frequency, consisting of an all-pass filter, two cascaded high-pass filters, and two cascaded low-pass filters, all also having the same first phase response.
20. The device of claim 13 , wherein: the all-pass filter is a Butterworth second-order infinite impulse response (IIR) filter; the third high-pass filter and the fourth high-pass filter are Butterworth second-order IIR filters; and the third low-pass filter and the fourth low-pass filter are Butterworth second-order IIR filters.
In the device of Claim 13, specific filter types are used. The all-pass filter is a Butterworth second-order IIR (Infinite Impulse Response) filter. The two cascaded high-pass filters applied to the second primary-stage output data are Butterworth second-order IIR filters. The two cascaded low-pass filters applied to the second primary-stage output data are Butterworth second-order IIR filters.
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March 28, 2016
March 28, 2017
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